Hip fracture is a devastating event. Within a year of the injury, 20-30% of patients die and 50% lose the ability to walk; in the United States these fractures account for 70% ($12 billion) of the direct annual costs of fracture care. Ironically, more than half of the women who sustain a hip fracture would not have qualified for osteoporosis treatment by the current criteria, which are based on bone mineral density (BMD) measurements by dual energy X-ray absorptiometry (DXA). Thus, a better approach is needed to determine if an individual is at risk for hip fracture from a fall. Biomechanically, a hip will fracture if the impact force resulting from a fall is greater than the bone strength. Therefore, th ability to determine hip strength is critical for fracture risk assessment. The current best non-invasive tool for direct hip strength assessment is based on quantitative computed tomography (QCT) guided finite element models. However, due to ionizing-radiation dose restrictions, the spatial resolution of clinical QCT (0.6-1 mm) is not sufficient to resolve bone microstructure at the hip. Leveraging our recent work, we propose to develop a novel method for assessing hip strength in vivo using magnetic resonance imaging (MRI) coupled with biomechanics. First, we propose to optimize our current MRI protocol for microstructural hip imaging to achieve 0.23-0.5 mm spatial resolution, and to reduce the finite element computation time to less than 30 minutes for predicting hip strength simulating a fall onto the hip on a desktop computer. Second, we propose to validate the accuracy of our MRI-derived hip strength technique by comparing the values obtained by this technique to the values obtained from the gold standard technique of mechanical testing of cadaveric femurs obtained from 30 donors. Third, we propose to apply the method optimized and validated above to determine if patients with hip fracture (N=40) have low bone strength for a fall onto the hip compared to matched healthy controls (N=40). We also propose to determine the test-retest reproducibility of MRI-derived strength by repeating the scanning and analysis in 10 healthy subjects. If further validated in longitudinal studies, the groundwork proposed under this project has the potential to introduce a paradigm shift for assessing hip fracture risk and monitoring the efficacy of osteoporosis treatment.